1. Field of the Invention
The present invention relates to a composition for abatement of pollution dispersed in the air and to an apparatus and a method using the composition. More specifically, the abatement composition of the invention comprises an intimate combination of first and second zeolites and an oxidation catalytic component. The abatement composition adsorbs and oxidizes volatile organic compounds, such as hydrocarbons, aldehydes, ketones, etc., in alternating adsorption and oxidation temperature ranges which lie within a low to moderate operating temperature range.
2. Related Art
A great deal of effort and a resulting large body of patent and technical literature is directed toward pollution abatement at its source, for example, by treating the exhaust of combustion devices such as internal combustion engine exhaust, plant stack gases, etc. Rather less effort has been devoted towards taking steps to clean the atmosphere, i.e., to treat ambient air to abate pollutants already contained therein. Illustrative of this latter approach is U.S. Pat. No. 3,738,088, "Mobile Air Cleaning Apparatus for Pollution Removal", issued on Jun. 12, 1973 to L. E. Colosimo. This patent discloses an air filtering assembly for abating ambient air pollution by providing duct work on a vehicle to direct an air stream of controlled velocity to various filter means to filter particulate pollutants from the air. Post-filter catalysts are also disclosed for catalytic abatement of ambient carbon monoxide, unburned hydrocarbons, nitrous oxide, sulfur oxides and the like. German Patent DE 43 18 738 C1, for "Verfahren zur physikalischen und chemischen Reinigung der Aussenluft" ("Method for the Physical and Chemical Cleaning of Atmospheric Air"), published on Jul. 14, 1994, similarly discloses a process for the physical and chemical cleaning of air utilizing a motor vehicle whose travel flows the air through the treatment devices.
U.S. Pat. No. 5,147,429, "Mobile Airborne Air Cleaning Station", issued on Sep. 15, 1992 to J. Bartholomew et al, discloses a dirigible carrying a plurality of different air-cleaning devices, including wet scrubbers, filtration machines and cyclonic spray scrubbers, to treat air which is flowed through the devices by movement of the dirigible through the air.
The use of a combination of adsorbents for hydrocarbons and a catalytic composition to promote the oxidation of the hydrocarbons is known in the art. For example, Japanese patent publication (Kokai) 8-10566 was published on Jan. 16, 1996 based on Japanese patent application of NGK Insulators, filed on Jul. 5, 1994 and entitled "A Catalyst Adsorbent For Purification of Exhaust Gases and An Exhaust Gas Purification Method." This document discloses the use of a silver-containing ZSM-5 zeolite and a platinum oxidation catalytic component for the treatment of the exhaust of internal combustion engines. At low exhaust temperature, such as that encountered upon initial startup of the engine, the silver-containing ZSM-5 zeolite adsorbs hydrocarbons in the exhaust and retains them until the temperature increases sufficiently to reach the light-off temperature of the platinum catalytic component, i.e., the temperature at which the catalytic component becomes effective for promoting oxidation of the hydrocarbons. Conventionally, the light-off temperature is considered to be that temperature at which the catalytic component is able to promote the oxidation of at least fifty percent of the hydrocarbons contacting the catalytic component. The objective of such compositions is to retain the hydrocarbons adsorbed in the adsorbent, typically zeolite, until a temperature of at least 250.degree. C. has been attained, so that upon desorption of the hydrocarbon at the elevated temperature, the catalytic component is effective for promoting oxidation of the hydrocarbon.